The primate frontal lobe consists of three main parts: the primary motor cortex (MI), the prefrontal cortex (PF), and the nonprimary motor cortex. The nonprimary motor cortex can be divided into at least two fields: the supplementary motor cortex (SM) and the premotor cortex (PM). Previous work on this project has clarified the definition of these cortical fields by an analysis of (a) neuronal responses to peripheral inputs, (b) thresholds for evoking movements with intracortical electrical stimulation, (c) the properties of single neurons during the performance of several visuomotor tasks, and (d) cytoarchitectonics. After preliminary definition of the areas, we used the techniques of behavioral neurophysiology, developed in the LNP, to study the functional organization of the caudal frontal lobe in primates. Our results support the hypothesis that, among their functions, PM and SM play a role in the preparation for future action. Many individual research projects have been designed and successfully executed to rule out alternatives to motor preparation (or 'set') as the functional correlate some activity we observe in PM and SM. However, we have recently found that not all PM activity is linked to motor functions. A study of "anticipatory discharges" in PM indicates that neuronal activity pattern does not reflect the preparation of movement and instead appears to play a role in anticipating the timing and/or nature of events.